1. Field of the Invention
This invention broadly relates to appliances that are used during the course of orthodontic treatment. More particularly, the present invention relates to an orthodontic appliance such as a bracket or molar appliance having a latch that releasably retains an archwire in an archwire slot.
2. Description of the Related Art
Orthodontic therapy is a specialized type of treatment within the field of dentistry, and involves movement of malpositioned teeth to orthodontically correct locations. Orthodontic treatment typically enhances the aesthetic appearance of the teeth, particularly in instances when the patient's front teeth are malpositioned or crooked. Orthodontic treatment can also improve the patient's occlusion so that the teeth interact better with each other during mastication.
Many type of orthodontic treatment programs involve the use of a set of tiny appliances and wires that are commonly known collectively as “braces”. During such treatment programs, small slotted appliances known as brackets are fixed to the patient's anterior, cuspid and bicuspid teeth, and an archwire is inserted into the slot of each bracket. The archwire forms a track to guide movement of the teeth to orthodontically correct locations. End sections of the archwires are typically captured in tiny appliances known as buccal tubes that are fixed to the patient's molar teeth.
Orthodontic brackets often have archwire slots that are open on one side for insertion of the archwire and that are bounded on remaining sides by walls or other structure of the brackets. Brackets that are affixed to the patient's buccolabial tooth surfaces (i.e., the surfaces of the teeth facing the patient's cheeks or lips) often have archwire slots that are open on a buccolabial side of the archwire slot. Brackets that are fixed to the lingual surfaces of the patient's teeth (i.e., the surfaces of the teeth facing the patient's tongue) often have an archwire slot that is open either on a lingual side or on an occlusal side (i.e., a side of the slot facing the outer tips of the teeth).
In the past, orthodontic practitioners commonly used elastomeric ligatures or wire ligatures to connect the archwire to the brackets and to urge the archwire into an orientation of seated engagement with the bottom of the archwire slot. Ligatures are typically installed by extending the ligature about the archwire as well as behind tiny protruding hooks known as “tiewings” that extend outwardly from a body of the bracket.
Recently, there has been increased interest in orthodontic appliances that have a latch for coupling the archwire to the appliance. Appliances of this type are widely known as self-ligating appliances and often obviate the need to use ligatures. A number of different latches are known, including movable clips, spring members, covers, shutters, bales and other structure. The latches are connected to a body of the appliance for releasably retaining the archwire in the archwire slot.
Improved self-ligating orthodontic appliances are described in two U.S. patents entitled “ORTHODONTIC APPLIANCE WITH SELF-RELEASING LATCH”, U.S. Pat. Nos. 6,302,688 and 6,582,226. The appliances described in those patents have a latch for retaining an archwire in the archwire slot, and the latch releases the archwire from the archwire slot whenever the archwire exerts a force on the appliance that exceeds a certain minimum value. The minimum value is significantly less than the force required in the same direction to debond the appliance from the tooth, and consequently helps to ensure that the appliance will not spontaneously debond from the tooth during the course of treatment.
In certain embodiments of the appliances described in the two U.S. patents mentioned above, the archwire may be inserted into the archwire slot by pressing the archwire against the latch. The latch is constructed to self-open without the need for hand instruments or other tools. Consequently, such appliances are a great advantage to the practitioner in that the time needed for connecting the archwire to the appliance can be significantly reduced.
In some of the appliances described in U.S. Pat. Nos. 6,302,688 and 6,582,226, the latch of the appliance comprises one or two resilient clips having a generally U-shaped configuration, and the clips spread open to admit an archwire into the archwire slot of the appliance. Preferably, the clips are made of a shape-memory alloy such as alloys of nitinol and beta-titanium in order to help assure that the clip reliably opens and closes as intended over extended periods of time. The use of shape-memory alloys also helps to ensure that the clip does not fracture during use so that the appliance need not be replaced once it is bonded to the patient's tooth.
However, clips that are made of nitinol and beta-titanium can present problems for the manufacturer during assembly of the appliance. For example, the resilient properties of such clips may be adversely affected if the clip is exposed to undue heat during assembly of the appliance, such as heat from a brazing or welding process. Brazing and welding processes are often used to join a base of the appliance, such as a mesh-type base, to a body of the appliance that has been separately manufactured.
Moreover, it is desirable to avoid increasing the overall size of the appliance when attempting to alter or improve the connection between the clip and remaining components of the appliance. An increase in the size of the appliance may increase the likelihood that the appliance will impinge on adjacent soft tissue in the oral cavity and cause discomfort to the patient. In addition, an increase in appliance size will often cause the appliance to be more visible to casual observers and adversely affect its aesthetic appearance.
Accordingly, it would be advantageous to provide a new self-ligating orthodontic appliance having improved means for connecting a clip of the appliance to remaining components of the appliance.